Check the count in the first word of __CTOR_LIST__ before executing

the loop that invokes the static constructors.  That makes it safe
to link c++rt0.o into any shared library, even one that does not
have any static constructors.  Formerly, doing that would cause a
bus error.  If the library has no static constructors, __CTOR_LIST__
comes out as a simple 4-byte COMMON region, and it does not have
the usual NULL word that terminates the list of constructors.  This
caused the old code to "call" a garbage address via the non-existent
entry __CTOR_LIST__[1].

The analogous code that invokes the static destructors was already safe.

This change is fully backward-compatible.

Reviewed by:	dfr@render.com (Doug Rabson)

1 files changed, 12 insertions, 4 deletions

diff --git a/lib/csu/i386/c++rt0.c b/lib/csu/i386/c++rt0.c
index aa28109..40cc5fa 100644
--- a/lib/csu/i386/c++rt0.c
+++ b/lib/csu/i386/c++rt0.c
@@ -27,7 +27,7 @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- *	$Id: c++rt0.c,v 1.2 1995/05/30 05:39:36 rgrimes Exp $
+ *	$Id: c++rt0.c,v 1.3 1995/06/27 09:53:24 dfr Exp $
  */
 
 /*
@@ -54,10 +54,18 @@ __dtors(void)
 static void
 __ctors(void)
 {
-	void (**p)(void) = __CTOR_LIST__ + 1;
+	/*
+	 * If the shared library doesn't have any static constructors in it,
+	 * then __CTOR_LIST__ will come out as a simple COMMON region of
+	 * 4 bytes.  That is why we have to check the count in the first
+	 * word.
+	 */
+	if ((unsigned long) __CTOR_LIST__[0] > 0) {
+		void (**p)(void) = __CTOR_LIST__ + 1;
 
-	while (*p)
-		(**p++)();
+		while (*p)
+			(**p++)();
+	}
 }
 
 extern void __init() asm(".init");